At present, reinforcement of a vehicle body side is generally achieved by coupling a side sill inner beam protruding from a lower portion of the inside of a vehicle body side panel towards the vehicle interior with a side sill outer beam protruding towards the vehicle interior to thereby form a side sill.
FIG. 1 is a view illustrating a vehicle body side reinforcement assembly according to the related art.
The vehicle body side reinforcement assembly according to the related art forms a cross-sectional “L”-shaped structure or  by connecting a first side reinforcement panel 10, a lower end portion of an inner center pillar 20, and a floor support 30 to one another, as illustrated in FIG. 1.
Because the vehicle body side reinforcement assembly is formed in the  structure, a collision load is not transferred to the floor support 30 forming a lower portion of a vehicle body when a side collision occurs. Because the load is transmitted through the vehicle body side, the safety performance of the vehicle body is degraded.
In addition, according to the related art, a side reinforcement assembly may include a bulkhead 40 to prevent the vehicle body from splitting when a side collision occurs, as shown in FIG. 1. In this configuration, an inner panel may be welded to be extended to a lower end portion of the side sill; however, when the side reinforcement assembly and the floor support 30 of the vehicle body are matched to each other, there is no room to insert a welding gun to weld the side reinforcement assembly and the floor support together. Without a weld in a horizontal direction in which the load is input when the side collision occurs, safety performance is degraded. Moreover, the constraints on space in this configuration require the use of costly additional materials, such as injected plastic to further reinforce the vehicle side, resulting in increased costs.